This application proposes to continue multidisciplinary studies of development, control and disorders of the pulmonary parenchyma. The objectives of the proposal are to examine some of the mechanisms involved in the formation and stabilization of the pulmonary parenchyma during development and post-natal life, and in states of health and disease. By stabilization we mean the integrated physiochemical and biological processes that develop and maintain alveolar architecture in an optimal state for pulmonary gas exchange. As in our past studies we emphasize investigations of alveolar epithelial development, functions of the lung surfactant system, and alveolar disease processes leading to infection and inflammation. The broad goals of the three inter-related projects proposed are: Project 1: Structure and function of surfactant proteins. To study the relationship between the structure of the surfactant proteins, specifically SP-D, and their functions in regulating the immune milieu of the alveolus. Project 2: Expression and role of CEACAM6 in the alveolus. To investigate the role of carcinoembryonic antigen-6 in alveolar innate immune defense, surfactant function, and epithelial response to acute lung injury. Project 3: Alveolar epithelial cell fates: mapping and regulation. To study alveolar epithelial cell lineages during development and regeneration and to elucidate novel regulatory molecules important to the process of alveolar epithelial differentiation. The overall purpose of these studies is to deepen our understanding of the processes underlying lung parenchymal stability and to contribute to new concepts and treatments for lung diseases associated with disorders of alveolar stability, growth, maturation, and repair after injury.